In recent months, a proposal to locate a casino at National Harbor, which is backed by Prince George’s County Executive Rushern L. Baker III (D), has crowded out discussion of Penn’s proposal to put a facility at Rosecroft, the harness track it owns in Fort Washington.

“To the best of my ability and to the limits of our corporate resources, we will fight furiously to stop this rush to create an exclusive opportunity for National Harbor until we have assurances that Rosecroft will be part of the mix of any expanded gaming in Prince George’s County,” Carlino wrote in a letter dated Monday, a copy of which was obtained by The Post.

Penn, a company based in Pennsylvania, has invested heavily in Maryland’s gambling program since its inception, contributing $2 million to support the campaign to legalize slots in 2008. The company also owns Hollywood Casino Perryville in Cecil County, which was the first casino to open in Maryland.

Having Penn on the other side in a potential campaign this fall could change the dynamic.

O’Malley is expected to announce any day now whether he will call a special legislative session next month to consider a plan that would both allow a Prince George’s casino and table games at Maryland’s five existing slots locations. Any such expansion would also require approval by voters statewide in November.

O’Malley aides have suggested that a plan would likely invite bids for a Prince George’s casino from a swath of the county that also includes Rosecroft. As with other Maryland casino locations, a commission would then be responsible for picking the best place.

Penn officials, however, say the deck is stacked heavily against them at this point.

“We believe that the playing field is unfair given the push by the county executive and the governor for a location at National Harbor,” said Penn National spokeswoman Karen Bailey. “It is for this reason that we oppose a special session and encourage the legislature to take it up during the regular session when all interested parties can present their plans under a clear set of rules where one is not openly favored over others or are making deals behind closed doors.”

In his letter, Carlino characterizes the National Harbor plan as “a clandestine agreement” reached between Baker and Milton V. Peterson, the developer of National Harbor.

“Once Mr. Baker went public with his planned partnership with Mr. Peterson, the issue of racing in Maryland was quickly forgotten,” Carlino wrote.

In the letter, Carlino also shares that Penn would be willing to build a more elaborate casino that initially advertised — spending $500 million instead of $300 million. That would put the company’s investment on par with that of the Cordish Cos., which opened Maryland Live! in Anne Arundel County last month.

Carlino also stressed that Penn is willing to to operate at the existing tax rate of 67 percent imposed on Maryland casino owners. National Harbor and MGM, the operators lined up at National Harbor, are advocating for a significantly lower rate.

“I do think that Penn National has conducted itself decently and professionally since the beginning of this gaming ad­ven­ture, spending millions of dollars at your request, to support the initial legislation, and being the first to invest, construct and open our facility in Perryville” Carlino wrote to O’Malley. “We want to be in Maryland, and we sincerely hope that you will help us achieve that.”

John Wagner is a national political reporter covering the White House. He previously covered the 2016 presidential election, focusing on the Democratic campaigns of Hillary Clinton, Bernie Sanders and Martin O’Malley. He also chronicled Maryland government for more than a decade.